Q&A

A P0303 is definitely related to #3 cylinder misfiring. Misfire conditions will cause the engine to run rough particularly at idle or under load. A misfire can be caused by the ignition (loss or insufficient spark, start by checking the plug), it can be caused by loss of fuel or lean mixture at #3 cylinder, (check the fuel injector. Using a mechanic's stethoscope (or use a long screw driver placing the handle end up to your ear place the metal tip end of the screwdriver against the body of the fuel injector), get a friend to crank over the engine while you "listen" to the fuel injector listen to each injector at the same point of the injector body. You should hear click, click, click as the injector is electrically opened and closed by the computer, if the injector is not being triggered you will not have fuel getting into the engines cylinders. Disconnect the electrical connector at the fuel injector with the ignition key in the "on" position, (next position after the accessory position) you should have 12 volts at one of the two wires at the injector. This true for most vehicles but you need to consult a workshop manual for your vehicle to see that this is true for your vehicle. When the engine is running the second wire at the injector gets grounded by the computer in your vehicle many times a second controlling exactly when and how much fuel gets injected into the engine), check the intake manifold at #3 make sure it is not allowing air in causing a lean running condition. After that you may need to check the compression in #3 to make sure the valves are sealing and cylinder id developing compression. Autozone have some popular workshop manuals for free on line once you register (for free) on their website http://bit.ly/autozone_repair_info or there is a company that independent auto repair shops "buy" their information from that offer a very reasonable service to do it yourselvers. You can get a one week subscription or year subscription very cheap. The information is year make and model specific repair procedures, service bulletins, component locations, wiring diagrams ect.... great quality information same as the professionals have ,much better than generic workshop manuals from parts stores, much cheaper than the factory manual try http://bit.ly/mitchell_repair_manuals_online
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